Microelectronic devices, such as metal devices, are playing an increasingly important role in our daily life. For instance, LEDs have become ubiquitous in many applications, such as mobile phones, appliances, and other electronic devices. Recently, the demand for nitride-based semiconductor materials (e.g., having gallium nitride or GaN) for opto-electronics has increased dramatically for applications ranging from video displays and optical storage to lighting and medical instruments.
Conventional blue LEDs are formed using compound semiconductor materials with nitride, such as GaN, AlGaN, InGaN, and AlInGaN. Most of the semiconductor layers of these light-emitting devices are epitaxially formed on electrically non-conductive sapphire substrates.